CRT, LCD (Liquid Crystal Device), DLP (Digital Light Processing Device), PDP, and the like are used as devices for color display, and RGB (red, green, and blue) three primary colors are used as general fundamental colors. On the other hand, white is also added in a part of LCD displays and DLP projectors to emphasize brightness.
That is, a display apparatus in which one pixel can display the color of four colors of R (red), G (green), B (blue), and W (white), and which displays RGB signals, which are inputted, by mixing the color of these four colors is used (e.g., refer to Japanese Patent Laid-Open No. 5-241551, and A. Kunzman and G. Pettitt, “White Enhancement for Color-Sequential DLP”, SID International Symposium Digest of Technical Papers, USA, SID (Society for Information Display), May, 1998, Vol 29, pp. 121-124). A display apparatus which displays one pixel in the color of four colors of RGBW in this way is used, for example in a direct-view liquid crystal display apparatus, a DLP projector, or the like. For example, a four-color wheel of RGBW is used in a field-sequential system of one-chip DLP data projector which uses a color wheel. In addition, four display elements, which can display four colors of RGBW, per pixel are used in a liquid crystal display apparatus.
By displaying each pixel not only using RGB but using W, in comparison with the case of displaying only by RGB, it is possible to perform bright display, to increase contrast, and to reduce the consumed power of a lamp when brightness is same.
The structure of such a conventional display apparatus 51 is shown in FIG. 28.
The display apparatus 51 is constituted of white color component detection instrument 7, white display element driving instrument 8, a white display unit 9, RGB display element driving instrument 10, and an RGB display unit 11.
The white color component detection instrument 7 is the instrument which detects a white color component from RGB signals inputted.
The white display element driving instrument 8 is the instrument which drives the white display unit 9 in order to display a white color component detected by the white color component detection instrument 7.
The white display unit 9 is the instrument which displays a white color component by being driven by the white display element driving instrument 8.
The RGB display element driving instrument 10 is the instrument which drives the RGB display unit 11 in order to display the RGB signals inputted.
The RGB display unit 11 is the instrument which displays RGB components by being driven by the RGB display element driving instrument 10.
Screen structure in the case that the display apparatus 51 is a liquid crystal display apparatus is shown in FIG. 29. Reference numeral 52 denotes a basic unit which constitutes one pixel, and is constituted of four liquid crystal cells which can independently control the extent of transmission of white light exposed from the back. Then, the four color filters of R, G, B, and W are located to these four liquid crystal cells, respectively. In this way, when the display apparatus 51 is a liquid crystal display apparatus, a screen of the RGB display unit 11 and white display unit 9 has structure as shown in FIG. 29.
In addition, when being a DLP projector, the display apparatus 51 has the structure that four colors of RGBW are time-sequentially switched and is displayed in one pixel of the screen while synchronizing with a color wheel. Thus, when the display apparatus 51 is a DLP projector, the RGB display unit 11 and white display unit 9 are constituted of the color wheel, DMD (Digital Micromirror Device), and the like.
Next, the operation of such the conventional display apparatus 51 will be explained.
The RGB signals inputted from an apparatus, which displays an image on the display apparatus 51, such as a personal computer, DVD equipment, or a TV receiver are inputted into the RGB display element driving instrument 10 and white color component detection instrument 7.
The RGB display element driving instrument 10 generates drive signals of the RGB display unit 11 in order to display the RGB signals inputted, and drives the RGB display unit 11 with the drive signals.
On the other hand, the white color component detection instrument 7 detects a white color component from the RGB signals inputted, and outputs the white color component to the white display element driving instrument 8. The white display element driving instrument 8 generates a drive signal of the white display unit 9 in order to display the white color component from white color component detection instrument 7, and drives the white display unit 9 with the drive signal.
The RGB display unit 11 displays three colors of R, G, and B by being driven by the RGB display element driving instrument 10. On the other hand, the white display unit 9 displays one color of W by being driven by the white display element driving instrument 8.
Since the white by the white display unit 9 is added to the white by the RGB display unit 11 in the display apparatus 51, brightness becomes nearly twice in comparison with the case of only the RGB display unit 11.
In this way, the display apparatus 51 can achieve the display of a full color image whose brightness and contrast are increased by four colors of the three primary RGB colors and white color.
Nevertheless, in the display apparatus 51, a luminance ratio of white to RGB becomes nearly two times as large also using the white display unit 9 in compared with the case of only the RGB display unit 11. In consequence, the difference in brightness between white and normal color may become so large that, it may be apart from the sense of brightness which the brain stores, and sense of incongruity may be felt as to the way those colors appear. Thus, the brightness of image portions of colors other than white becomes dark relatively in comparison with the brightness of a white portion. As a result, since the brightness of some colors is much different from that of a white portion, the colors appear differently, and hence, sense of incongruity arises.
Since the luminance ratio of white and bright yellow becomes large in particular, yellow looks darker and the difference from the memory color of yellow becomes large, and hence, the sense of incongruity becomes large. Thus, as shown in FIG. 30, when pixels 14 in pastel yellow which are bright yellow, and pixels 13 in white which are white are displayed on the display screen, the bright yellow looks darker due to the contract with the white and the bright yellow may appear greenish. Such the sense of incongruity arises similarly also in bright cyan or bright magenta.
Thus, a display apparatus in which one pixel can be displayed in the color of four colors, that is, the three primary colors and a white color, and which inputs and displays chrominance signals corresponding to the mixing ratio of the color of the four colors has a problem that the brightness of colors may be apart from those which a brain stores when the difference in brightness between white and normal colors becomes large, and the sense of incongruity may be felt as to the way normal colors appear.